Factors Determining the Efficacy of Botulinum Toxin for Arm Tremor in Dystonia

Inclusion Criteria: * Clinical diagnosis of dystonic tremor or tremor associated with dystonia according to the 2018 consensus statement on the classification of tremors * Tremor of one or both upper extremities * Starting botulinum toxin injections as part of normal clinical practice * Age ≥ 18 years Exclusion Criteria: * Acquired aetiology of dystonic tremor syndrome * Previous botulinum toxin treatment of the to be treated upper extremity for ≥ 4 consecutive sessions * In case of previous botulinum toxin treatment of the to be treated upper extremity for ≤3 consecutive sessions: the last botulinum toxin injections ≤ 6 months before study enrolment * Unstable dose medications for dystonia and tremor ≤ 1 month before study enrolment * Deep brain stimulation implantation ≤ 6 months before study enrolment * Unstable deep brain stimulation variables ≤ 1 month before study enrolment * Comorbidity interfering with study participation * Known hypersensitivity for components of Dysport * Infection at the upper extremity * Pregnancy, trying to conceive and breastfeeding * Insufficient knowledge of the Dutch or English language Exclusion criteria for MRI scanning: * Contraindications for MRI (e.g. previous brain surgery, claustrophobia, active implant, epilepsy, metal objects in the upper body that are incompatible with MRI) * Moderate to severe head tremor while lying supine (to avoid artefacts caused by extensive head motion during scanning). * Inability to provoke postural tremor while lying supine.